Network connection system and traffic shaping method for facilitating shaping traffic even in network which accommodates lines based on different protocols

ABSTRACT

A packet scheduling apparatus corrects an overhead amount between a DSL rate and a packet rate, converts DSL rate information to the packet rate, and shapes the IP packets from the Internet such that the IP packets are delivered at a transmission rate equal to or lower than the packet rate. An IP/ATM converter converts the IP packets from the packet scheduling apparatus to ATM cells. A DSL multiplexer has a DSL current rate detector for supplying DSL rate information indicative of a currently set DSL rate, and transmits the ATM cells from the IP/ATM converter or the IP packets from the packet scheduling apparatus to user terminals through DSL processing using telephone lines.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a network connection system forconnecting a communication network and a plurality of user terminals,and more particularly, to a traffic shaping method for shaping thetransmission rate for IP packets from the Internet which is one type ofIP network.

[0003] 2. Description of the Related Art

[0004] In recent years, a variety of DSL techniques, represented by ADSL(Asynchronous Digital Subscriber Line), have become increasingly popularbecause of the ability to make a high speed connection with theInternet.

[0005]FIG. 1 illustrates the configuration of a conventional networkconnection system which employs such a DSL technique.

[0006] In the illustrated conventional system, user terminal 5 such as apersonal computer is connected to Internet 7, which is an IP network,through a telephone central office 106. Then, telephone central office106 is equipped therein with IP (Internet Protocol)/ATM (AsynchronousTransfer Mode) converter 3 and DSL multiplexer 101 which areinterconnected through ATM network 2. While FIG. 1 illustrates that onlyone user terminal 5 is connected to DSL multiplexer 101, a large numberof user terminals are actually connected to DSL multiplexer 101 throughrespective telephone lines.

[0007] IP/ATM converter 3 acts as a protocol converter for converting IPpackets from Internet 7 to ATM cells.

[0008] DSL multiplexer 101 performs telephone line-based DSL processingby multiplexing and demultiplexing with a large number of user terminals5, termination, and the like.

[0009] Such a network connection system enables high speed datacommunications between user terminal 5 and Internet 7 using a telephoneline without the need for providing a special line to user terminal 5.

[0010] Also, in the DSL technique, a bandwidth is set for use inhand-shaking for setting a DSL line. For this purpose, DSL multiplexer101 shapes cells to be transmitted such that the transmission rate ofmultiplexed ATM cells will not exceed the set DSL bandwidth. The shapingrefers to a function of adjusting the transmission rate of cells inaccordance with a set bandwidth, and is implemented, for example, usinga token buffer.

[0011] In the conventional system, DSL multiplexer 101 shapes thetransmission rate for ATM cells to be transmitted to user terminal 5with a bandwidth (transmission rate) which has been set in the event ofhand-shaking. However, since the telephone line situation fluctuates dueto the influence of external noise and the like, techniques have beenproposed for changing a used bandwidth while a line is in connection.

[0012] Japanese patent laid open No. 10-84346, for example, discloses adynamic shaping apparatus which changes the rate at which cells areshaped, corresponding to a change in the rate even when a set bandwidthis changed during a connection of a line as mentioned above,

[0013] In the conventional network connection system described above, IPpackets from Internet 7 are converted to ATM cells by IP/ATM converter 3before they are transmitted to user terminal 5 through DSL multiplexer101. However, IP packets from Internet 7 are transmitted to userterminal 5 as is without conversion to ATM cells.

[0014] The conventional network connection system illustrated in FIG. 1relies on a cell-based DSL technique, wherein IP packets transmitted totelephone central office 106 through Internet 7 are converted to ATMcells in IP/ATM converter 3, followed by a transfer of the ATM cells touser terminal 5. In recent years, however, a packet-based DSL techniquehas been proposed for transferring IP packets from Internet 7 to userterminal 5 without conversion of the IP packets to ATM cells. However,since DSL multiplexer 101 must accommodate as many as approximately1000-2000 user terminals, cell-based DSL will be mixed with packet-basedDSL.

[0015]FIG. 2 illustrates another conventional network connection systemas mentioned above. In the system illustrated in FIG. 2, telephonecentral office 206 is equipped with DSL multiplexer 201. This DSLmultiplexer 201 is capable of directly transmitting IP packets fromInternet 7 to user terminal 5. However, when DSL multiplexer 201accommodates a mixture of cell-based DSL and packet-based DSL in thisway, complicated processing is required for controlling DSL multiplexer201 such that the transmission rate of data transmitted to user terminal5 falls within the previously set DSL rate in a method similar tobefore. The reason will be discussed below as to the requirement ofcomplicated processing.

[0016] As shown in FIG. 3, each of ATM cells is provided with a headerwhen IP packets are converted to ATM cells. With the header added toeach ATM cell, the IP packets differs from the ATM cells in thetransmission rate even if the same data is to be transmitted. For thisreason, the ATM cells and IP packets cannot be controlled for shaping onthe same basis, resulting in the need for the shaping control conductedwith different bases, respectively.

[0017] Further, in recent years, a variety of Internet-based serviceshave been proposed and utilized, including IP telephone, viewing ofmoving images, and the like. However, a problem will arise if a varietyof such services are provided in the same communication quality. While aslight delay will not cause a problem with such services as viewing ofWeb pages and E-mail, interrupted transmission of data during IPtelephone or viewing of a moving image would threaten the establishmentof such services. It is therefore necessary to change the communicationquality based on the contents of provided services.

[0018] To meet this requirement, conventionally, a constant bit rate(CBR) service has been applied to services such as the IP telephone andviewing of moving image, for which a constant communication qualityshould be ensured, to assign a constant cell rate, while a variable bitrate (VBR) service has been applied to services such as a Web pagesearch for which a certain transmission rate need not be ensured.

[0019] It is contemplated, however, that a variety of types of serviceswill be provided through the Internet as well in the future. Presumably,a variety of guaranteed class services will be provided through the sameline, such as services for which a minimum rate is guaranteed, inaddition to simply those services which are provided with priority, andbest-effort services which are not provided with priority.

[0020] However, in the conventional system described above, complicatedprocessing is involved if DSL multiplexer 201 processes data conformingto two different protocols, i.e., ATM cells and IP packets which cannotbe controlled in accordance with the same basis, while a minimum rate isguaranteed for a particular service. The conventional system wouldtherefore encounter difficulties in implementing a QoS (Quality ofService) control with a variety of quality guaranteed classes settherein.

[0021] Further, in the conventional network connection system, as thenumber of user terminals 5 increases, a plurality of DSL multiplexers201 are additionally provided for accommodating extra lines. However,since the traffic must be shaped in each of the plurality of DSLmultiplexers 201, a resulting increase in a management cost and adevelopment cost will impede a reduction in overall cost.

SUMMARY OF THE INVENTION

[0022] It is an object of the present invention to provide a networkconnection system which facilitates the shaping in accordance with a setDSL rate when a cell-based DSL and a packet-based DSL are accommodatedin mixture.

[0023] It is another object of the present invention to provide anetwork connection system which is capable of accommodating a mixture ofa cell-based DSL and a packet-based DSL, preventing a rate aftermultiplexing from exceeding a set DSL rate when a variety of qualityguaranteed classes of services are multiplexed for transmission, andrealizing services of minimum rate guaranteed class.

[0024] To achieve the above objects, the present invention provides anetwork connection system for connecting a first communication networkand a plurality of user terminals when a second communication network isinterposed between the first communication network and the plurality ofuser terminals, wherein the second communication network employs asecond protocol different from a first protocol employed in the firstcommunication network. The system includes a scheduling apparatus, aprotocol converter, and a multiplexer.

[0025] The scheduling apparatus has an overhead amount correction unitfor correcting an overhead amount between data conforming to the secondprotocol and data conforming to the first protocol to convert receivedinformation on a rate based on the second protocol to a rate based onthe first protocol, and a scheduler for shaping a transmission rate fordata conforming to the first protocol from the first communicationnetwork such that the data conforming to the first protocol is deliveredat a transmission rate equal to or lower than the rate calculated by theoverhead amount correction unit.

[0026] The protocol converter converts the data conforming to the firstprotocol after the scheduling apparatus has shaped the transmission ratetherefor to data conforming to the second protocol for use in the secondnetwork.

[0027] The multiplexer has a current data detector for supplying thescheduling apparatus with the rate information as indicative of acurrently set reception rate for the user terminals, transmits to eachof the user terminals the data conforming to the second protocol fromthe protocol converter or the data conforming to the first protocolafter the scheduling apparatus has shaped the transmission ratetherefor.

[0028] In the present invention, the current reception rate set for theuser terminals, notified by the current rate detector, is converted tothe rate based on the second protocol by the overhead amount correctionunit of the scheduling apparatus. Then, this rate is relied on by theprotocol converter to shape the transmission rate for the dataconforming to the first protocol before the conversion to the dataconforming to the second protocol. In consequence, even when themultiplexer accommodates a mixture of lines based on the second protocoland lines based on the first protocol, the shaping can be readilyaccomplished in accordance with a set reception rate.

[0029] Another network connection system according to the presentinvention includes a scheduling apparatus, a protocol converter, and amultiplexer.

[0030] The scheduling apparatus further has a classification processingunit, an overhead amount correction unit, a weighting coefficientcalculation unit, a weighting scheduler, and a preferential controlscheduler.

[0031] The classification processing unit classifies data conforming tothe first protocol received from the communication network based onquality guaranteed classes set thereto.

[0032] The overhead amount correction unit corrects an overhead amountbetween a data rate associated with the first protocol and a data rateassociated with the second protocol to convert received rate informationon the second protocol to the rate based on the first protocol.

[0033] The weighting coefficient calculation unit calculates a weightingcoefficient based on the rate calculated by the overhead amountcorrection unit such that a minimally guaranteed rate is assured for aminimum rate guaranteed class among classes classified by theclassification processing unit.

[0034] The weighting scheduler schedules data conforming to the firstprotocol of the minimum rate guaranteed class and of a weighting appliedclass among the classified classes based on the weighting coefficientcalculated by the weighting coefficient calculation unit to deliver thedata in accordance with the scheduling.

[0035] The preferential control scheduler schedules the data conformingto the first protocol from the weighting scheduler, and data conformingto the first protocol of a best-effort class among the classifiedclasses such that the data conforming to the first protocol is deliveredat a transmission rate equal to or lower than the rate calculated by theoverhead amount correction unit, preferentially schedules the dataconforming to the first protocol from the weighting scheduler, anddelivers the data conforming to the first protocol of the best-effortclass at a timing at which there is no data conforming to the firstprotocol from the weighting scheduler.

[0036] The protocol converter converts the data conforming to the firstprotocol after the scheduling apparatus has shaped the transmission ratetherefor to data conforming to the second protocol.

[0037] The multiplexer has a current data detector for supplying thescheduling apparatus with the rate information as indicative of acurrently set reception rate for the user terminals, and transmits toeach of the user terminals the data conforming to the second protocolfrom the protocol converter or the data conforming to the first protocolafter the scheduling apparatus has shaped the transmission ratetherefor.

[0038] In the present invention, the current DSL rate notified by theDSL current rate detector is converted to a packet rate by the overheadamount correction unit of the packet scheduling apparatus, and thispacket rate is relied on by an IP/ATM converter to shape thetransmission rate for IP packets before they are converted to ATM cells.Thus, even when the multiplexer accommodates a mixture of a cell-basedDSL and a packet-based DSL, the shaping can be readily accomplished inaccordance with a set DSL rate. Further, according to the presentinvention, since the weighting coefficient is calculated for a minimumrate guaranteed class based on a packet rate calculated by the overheadamount correction unit, the network connection system can readilyprovide services belonging to the minimum rate guaranteed class whilepreventing the transmission rate after multiplexing from exceeding theset DSL rate.

[0039] In another network connection system according to the presentinvention, a scheduling apparatus includes a classification processingunit, a rate measuring unit, an overhead amount correction unit, aweighting coefficient calculation unit, a weighting scheduler, and apreferential control scheduler.

[0040] The classification processing unit classifies data conforming tothe first protocol received from the communication network based onquality guaranteed classes set thereto.

[0041] The rate measuring unit measures a transmission rate for apreferential class among the classified classes.

[0042] The overhead amount correction unit corrects an overhead amountbetween a rate based on the second protocol and a rate based on thefirst protocol to convert received rate information on the secondprotocol to the rate based on the first protocol.

[0043] The weighting coefficient calculation unit calculates a weightingcoefficient based on the rate calculated by the overhead amountcorrection unit and the transmission rate for the preferential classmeasured by the rate measuring unit such that a minimally guaranteedrate is assured for a minimum rate guaranteed class among the classesclassified by the classification processing unit.

[0044] The weighting scheduler schedules data conforming to the firstprotocol of the minimum rate guaranteed class and of a weighting appliedclass among the classified classes based on the weighting coefficientcalculated by the weighting coefficient calculation unit to deliver thedata in accordance with the scheduling.

[0045] The preferential control scheduler schedules the data conformingto the first protocol of the preferential class, the data conforming tothe first protocol from the weighting scheduler, and data conforming tothe first protocol of a best-effort class among the classified classessuch that the data conforming to the first protocol is delivered at atransmission rate equal to or lower than the rate calculated by theoverhead amount correction unit. The preferential control schedulerfurther preferentially schedules the data conforming to the firstprotocol of the preferential class, preferentially schedules the dataconforming to the first protocol from the weighting scheduler at atiming at which there is no data conforming to the first protocol of thepreferential class, and delivers the data conforming to the firstprotocol of the best-effort class at a timing at which there is no dataconforming to the first protocol from the weighting scheduler.

[0046] According to the present invention, even with the introduction ofa preferential class which must be processed with the highest priority,a weighting coefficient is calculated for the minimum rate guaranteedclass in consideration of the transmission rate for the preferentialclass, the minimum rate can be assured for the minimum rate guaranteedclass while the preferential class is processed with the highestpriority.

[0047] In another network connection system according to the presentinvention, a scheduling apparatus includes a classification processingunit, a rate measuring unit, an overhead amount correction unit, apreferential class upper limit setting unit, a weighting coefficientcalculation unit, a weighting scheduler, and a preferential controlscheduler.

[0048] The classification processing unit classifies data conforming tothe first protocol received from the communication network based onquality guaranteed classes set thereto.

[0049] The rate measuring unit measures a transmission rate for apreferential class among the classified classes.

[0050] The overhead amount correction unit corrects an overhead amountbetween a rate based on the second protocol and a rate based on thefirst protocol to convert received rate information on the secondprotocol to the rate based on the first protocol.

[0051] The preferential class upper limit setting unit is operative whenthe difference between the transmission rate of the data conforming tothe first protocol of the preferential class as measured by the ratemeasuring unit and the rate calculated by the overhead amount correctionunit is lower than a minimally guaranteed rate for a minimum rateguaranteed class among the classes classified by the classificationprocessing unit, and sets an upper limit to the transmission rate forthe preferential class for shaping such that the minimally guaranteedrate can be assured for the minimum rate guaranteed class.

[0052] The weighting coefficient calculation unit calculates a weightingcoefficient based on the rate calculated by the overhead amountcorrection unit and the transmission rate for the preferential classmeasured by the rate measuring unit such that a minimally guaranteedrate is assured for the minimum rate guaranteed class among the classesclassified by the classification processing unit when the preferentialclass upper limit setting unit does not set the upper limit, andcalculates a weighting coefficient based on the rate calculated by theoverhead amount correction unit and the upper limit rate set by thepreferential class upper limit setting unit such that the minimallyguaranteed rate is assured for the minimum rate guaranteed class whenthe preferential class upper limit setting unit sets the upper limit.

[0053] The weighting scheduler schedules data conforming to the firstprotocol of the minimum rate guaranteed class and of a weighting appliedclass among the classified classes based on the weighting coefficientcalculated by the weighting coefficient calculation unit to deliver thedata in accordance with the scheduling.

[0054] The preferential control scheduler schedules the data conformingto the first protocol of the preferential class, the data conforming tothe first protocol from the weighting scheduler, and data conforming tothe first protocol of a best-effort class among the classified classessuch that the data conforming to the first protocol is delivered at atransmission rate equal to or lower than the rate calculated by theoverhead amount correction unit. The preferential control schedulerfurther preferentially schedules the data conforming to the firstprotocol of the preferential class, preferentially schedules the dataconforming to the first protocol from the weighting scheduler at atiming at which there is no data conforming to the first protocol of thepreferential class, and delivers the data conforming to the firstprotocol of the best-effort class at a timing at which there is no dataconforming to the first protocol from the weighting scheduler.

[0055] The multiplexer in the present invention includes a current ratedetector for supplying the scheduling apparatus with a currently setreception rate for the user terminals as information on the rate of thesecond protocol, and transmits data conforming to the second protocolfrom the protocol converter, or the data conforming to the firstprotocol after the shaping by the scheduling apparatus to each userterminal through DSL processing using a telephone line.

[0056] According to the present invention, though an upper limit isimposed to the preferential class, the minimum rate can be assured forthe minimum rate guaranteed class without fail even when thepreferential class is introduced into the network.

[0057] Alternatively, in the present invention, the preferential classupper limit setting unit and weighting coefficient calculation unit mayknow the transmission rate for the preferential class using informationfed back from the user terminals without providing the rate measuringunit.

[0058] Further, in the present invention, the current rate detector mayperiodically apply the rate information to the scheduling apparatus atregular time intervals, or may apply the rate information to thescheduling apparatus upon update of the reception rate set for the userterminals. Alternatively, the current rate detector may supply thescheduling apparatus with the rate information as indicative of areception rate for the user terminal set between a user terminal and themultiplexer in the event of hand-shaking.

[0059] The above and other objects, features and advantages of thepresent invention will become apparent from the following descriptionwith reference to the accompanying drawings which illustrate examples ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0060]FIG. 1 is a block diagram illustrating the configuration of aconventional network connection system;

[0061]FIG. 2 is a block diagram illustrating the configuration ofanother conventional network configuration system;

[0062]FIG. 3 is a diagram for describing the difference in overheadamount in the transmission rate between IP packets and ATM cells;

[0063]FIG. 4 is a block diagram illustrating the configuration of anetwork connection system according to a first embodiment of the presentinvention;

[0064]FIG. 5 is a block diagram illustrating the configuration of packetscheduling apparatus 4 in FIG. 4;

[0065]FIG. 6 is a block diagram illustrating the configuration of packetscheduling apparatus 34 in a network connection system according to asecond embodiment of the present invention; and

[0066]FIG. 7 is a block diagram illustrating the configuration of packetscheduling apparatus 44 in a network connection system according to athird embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0067] First Embodiment:

[0068]FIG. 4 is a block diagram illustrating the configuration of anetwork connection system according to a first embodiment of the presentinvention. In FIG. 4 components identical to those in FIG. 2 aredesignated the same reference numerals, and repeated description thereonis omitted.

[0069] In the network connection system of the first embodiment, userterminal 5 is connected to Internet 7 through telephone central office6.

[0070] Telephone central office 6 in the first embodiment is providedwith packet scheduling apparatus 4 between Internet 7 and IP/ATMconverter 3, and DSL multiplexer 201 in FIG. 2 is replaced with DSLmultiplexer 1.

[0071] DSL multiplexer 1 differs from DSL multiplexer 201 in theconventional network connection system illustrated in FIG. 2 in that DSLcurrent rate detector 20 is provided.

[0072] DSL current rate detector 20 delivers DSL rate information 10which represents a current DSL rate set between DSL multiplexer 1 anduser terminal 5, i.e., a reception rate of user terminal 5.

[0073] Here, DSL current rate detector 20 may periodically deliver DSLrate information 10 at regular time intervals, or delivers DSL rateinformation 10 when the set DSL rate is changed. Alternatively, DSLcurrent rate detector 20 may apply packet scheduling apparatus 4 withDSL rate information 10 which represents a DSL rate set between DSLmultiplexer 1 and user terminal 5 upon hand-shaking.

[0074] Next, FIG. 5 illustrates the configuration of packet schedulingapparatus 4 in FIG. 4. The following description is made on theassumption that Classes 1-3 are set for quality guaranteed classes.Class 1 is a quality guaranteed class which is guaranteed a minimumrate, wherein Class 1 is guaranteed that the transmission rate will notbe equal to or lower than minimally guaranteed rate V. Class 2 is aweighting applied class which is not provided with the quality guaranteeas above, but is guaranteed a quality higher than the best-effort class.Class 3 is the best-effort class which is not guaranteed the quality.

[0075] As illustrated in FIG. 5, packet scheduling apparatus 4 comprisesoverhead amount correction unit 11, preferential control scheduler 12,weighting scheduler 13, and classification processing unit 14.

[0076] Classification processing unit 14 classifies IP packets receivedfrom Internet 7 based on the set quality guaranteed classes.

[0077] Overhead amount correction unit 11 corrects an overhead amountbetween the DSL rate and packet rate to convert DSL rate information 10from current rate detector 20 in DSL multiplexer 1 to a packet rate.Here, description is made on the assumption that the packet rate isindicated by C (bps) after the DSL rate communicated by DSL rateinformation 10 has been corrected for the overhead amount.

[0078] Weighting coefficient calculation unit 15 calculates weightingcoefficients W1, W2 based on packet rate C calculated by overhead amountcorrection unit 11 so as to guarantee minimally guaranteed rate V (bps)for Class 1 which is the minimum rate guaranteed class.

[0079] For example, when packet rate C is exceeded by a total of thetraffic of Class 1 which is guaranteed the minimum rate and Class 2which is not guaranteed the minimum rate, but is only applied withweighting, weighting coefficient calculation unit 15 calculatesweighting coefficient W1 for Class 1 and weighting coefficient W2 forClass 2 which is not guaranteed the minimum rate by the followingequations:

W 1=V/C, W 2=1−W 1

[0080] In another case, where Class 1 and Class 2 are guaranteed minimumrates V1 and V2, respectively, but packet rate C is not exceeded by atotal of the traffic of Class 1 and Class 2, weighting coefficientcalculation unit 15 may assign weighting coefficients W1, W2 for Classes1, 2 in proportion to minimally guaranteed rates V1, V2, respectively:

W 1=V 1/(V 1+V 2), W 2=V 2/(V 1+V 2)

[0081] In a further case, where packet rate C is not exceeded by a totalof the traffic of Class 1 and Class 2, Classes 1 and 2 are guaranteedminimum rates V1, V2, respectively, but a residual bandwidth ispreferentially allocated to Class 1, weighting coefficient calculationunit 15 may calculate weighting coefficients W1, W2 for Classes 1, 2 asexpressed by the following equations:

W 2=V/C, W 1=1−W 2

[0082] While several specific examples have been shown above for thecalculation of weighting coefficients W1, W2, the present invention isnot limited to this method of calculating the weighting coefficients.The present invention can be applied to any calculation, method as longas weighting coefficient calculation unit 15 calculates weightingcoefficients based on packet rate C calculated by overhead amountcorrection unit 11 so as to guarantee the minimally guaranteed rate fora class which should be guaranteed the minimum rate.

[0083] Weighting scheduler 13 schedules IP packets of Class 1 and Class2 based on weighting coefficients W1, W2 calculated by weightingcoefficient calculation unit 15, and delivers the IP packets topreferential control scheduler 12.

[0084] Specific weighting method used herein may be a round-robin basedweighting method, and the like.

[0085] Preferential control scheduler 12 schedules the IP packets fromweighting scheduler 13 and IP packets of Class 3 which is thebest-effort class, such that the transmission rate of IP packets to bedelivered is equal to or lower than packet rate C calculated by overheadamount correction unit 11. Also, preferential control scheduler 12preferentially schedules IP packets from weighting scheduler 13, anddelivers IP packets of Class 3, which is the best-effort class, at atiming at which no IP packet is delivered from weighting scheduler 13.

[0086] Preferential control scheduler 12 may be implemented, forexample, by using a token buffer which is provided with tokens at packetrate C calculated by overhead amount correction unit 11, and controllingthe resulting rate.

[0087] Next, the operation in the network connection system according tothe first embodiment will be described with reference to the drawings.

[0088] The following description is made on the assumption that Class 1,which is the minimum rate guaranteed class, is guaranteed minimum rate Vof 5 M (bps).

[0089] First, in DSL multiplexer 1, DSL current rate detector 20transmits DSL rate information 10 which represents the currently set DSLrate to packet scheduling apparatus 4. Assume herein that the currentDSL rate is set at 8 M(bps).

[0090] Upon receipt of DSL rate information 10 from DSL multiplexer 1,packet scheduling apparatus 44 converts the DSL rate detected inoverhead amount correction unit 11 to a packet rate. Assume herein thatsince the current DSL rate is 8 M (bps), packet rate C corrected for theoverhead amount is calculated to be 7 M (bps).

[0091] Then, weighting coefficient calculation unit 15 calculatesweighting coefficient W1 for Class 1 as W1=5/7 because minimallyguaranteed rate V for Class 1 is 5 M (bps). Further, weightingcoefficient calculation unit 15 calculates weighting coefficient W2 forClass 2 as W2=1−5/7=2/7.

[0092] Weighting scheduler 13 schedules IP packets of Class 1 and IPpackets of Class 2 based on weighting coefficients W1 (=5/7), W2 (=2/7)calculated by weighting coefficient calculation unit 15, and deliversthe IP packets to preferential control scheduler 12. Preferentialcontrol scheduler 12 shapes the IP packets from weighting scheduler 13with packet rate C (=7M (bps)) calculated by overhead amount correctionunit 11, and delivers the shaped IP packets.

[0093] As previously described, in the network connection system of thisembodiment, the current DSL rate notified by current rate detector 20 isconverted to packet rate C by overhead amount correction unit 11 ofpacket scheduling apparatus 4, and this packet rate C is relied on toshape the transmission rate of the IP packets before they are convertedto ATM cells in IP/ATM converter 3, so that the shaping can be readilyperformed in accordance with the set DSL rate even if a cell-based DSLand a packet-based DSL are accommodated in mixture.

[0094] Also, according to the network connection system of thisembodiment, since the weighting coefficient is calculated for Class 1,which is guaranteed the minimum rate, based on packet rate C calculatedby overhead amount correction unit 11, services in the minimum rateguaranteed class can be readily provided while the transmission rateafter multiplexing is prevented from exceeding the set DSL rate.

[0095] Second Embodiment:

[0096] Next, description will be Made on a network connection systemaccording to a second embodiment of the present invention with referenceto FIG. 6.

[0097] The network connection system of the second embodiment has packetscheduling apparatus 34 shown in FIG. 6 which is substituted for packetscheduling apparatus 4 in the network connection system of the firstembodiment illustrated in FIG. 4.

[0098] The configuration of packet scheduling apparatus 34 in thenetwork connection system according to the second embodiment of thepresent invention will be described with reference to a block diagram ofFIG. 6. In FIG. 6, components identical to those in FIG. 5 aredesignated the same reference numerals, and repeated description thereonis omitted.

[0099] The second embodiment provides an additional quality guaranteedclass, i.e., Class 0 which is the most preferential class which isprocessed with the highest priority, in addition to Classes 1, 2, 3described in the first embodiment.

[0100] Packet scheduling apparatus 34 in the second embodiment differsfrom packet scheduling apparatus 4 illustrated in FIG. 5 in thatpreferential control scheduler 32 is substituted for preferentialcontrol scheduler 12, weighting coefficient calculation unit 35 issubstituted for weighting coefficient calculation unit 15, and ratemeasuring unit 36 is additionally provided.

[0101] Rate measuring unit 36 measures transmission rate r (bps) forClass 0, which is the most preferential class, and supplies transmissionrate r to weighting coefficient calculation unit 35. Since specificmeans for measuring the transmission rate can be implemented by ageneral expedient, detailed description thereon is omitted here.

[0102] Weighting coefficient calculation unit 35 stores transmissionrate r of Class 0 measured by rate measuring unit 36, and calculatesweighting coefficients W1, W2 based on packet rate C calculated byoverhead amount correction unit 11 and stored transmission rate r forClass 0, such that minimally guaranteed rate V (bps) is ensured forClass 1 which is a minimum rate guaranteed class.

[0103] Specifically, weighting coefficient calculation unit 35calculates weighting coefficient W1 for Class 1 which is guaranteed theminimum rate, for example, by the following equation:

W 1=V/(C−r)

[0104] Then, weighting coefficient calculation unit 35 calculatesweighting coefficient W2 for Class 2, which is not guaranteed theminimum rate, by the following equation in a manner similar to theaforementioned first embodiment:

W 2=1−W 1

[0105] In a case, where Class 1 and Class 2 are guaranteed the minimumrates V1 and V2, respectively, but the total traffic of Class 1 andClass 2 will not exceed rate C−r which is calculated by subtractingtransmission rate r for Class 0 from packet rate C, weightingcoefficient calculation unit 35 may apply weighting coefficients W1, W2to Classes 1, 2 in proportion to minimally guaranteed rates V1, V2:

W 1=V 1/(V 1+V 2),

W 2=V 2/(V 1+V 2)

[0106] In a further case, where rate C−r is not exceeded by the totaltraffic of Class 1 and Class 2, Class 1 and Class 2 are guaranteedminimum rates V1, V2, respectively, but a residual bandwidth ispreferentially allocated to Class 1, weighting coefficient calculationunit 35 may calculate weighting coefficients W1, W2 for Classes 1, 2 asexpressed by the following equations:

W 2=(V−r)/C,

W 1=1−W 2

[0107] While several specific examples have been shown above for thecalculation of weighting coefficients W1, W2, the present invention isnot limited to this method of calculating the weighting coefficients.The present invention can be applied to any calculation method as longas weighting coefficient calculation unit 35 calculates weightingcoefficients based on packet rate C calculated by overhead amountcorrection unit 11 and transmission rate r for Class 0 measured by ratemeasuring unit 36 so as to guarantee the minimally guaranteed rate for aclass which should be guaranteed the minimum rate.

[0108] Preferential control scheduler 32 processes IP packets of Class0, which is the most preferential class, with the highest priority, andschedules IP packets from weighting scheduler 13 and IP packets of Class3 through similar processing to preferential control scheduler 12 in thefirst embodiment in a empty band in which there are no IP packets ofClass 0.

[0109] Specifically, preferential control scheduler 32 preferentiallyschedules IP packets of Class 0; preferentially schedules IP packetsfrom weighting scheduler 13 in a band in which there are no IP packetsof Class 0; and delivers IP packets of Class 3, which is a best-effortclass, at a timing at which there are no IP packets from weightingscheduler 13.

[0110] Preferential control scheduler 32 further schedules IP packets ofthe preferential class, IP packets from weighting scheduler 13, and IPpackets of best-effort Class 3 such that the transmission rate of IPpackets delivered therefrom is equal to or lower than packet rate Ccalculated by overhead amount correction unit 11.

[0111] The network connection system according to the second embodimentcan also support a preferential class which must be processed with thehighest priority, and ensure the minimum rate for Class 1, whileprocessing IP packets of Class 0 with the highest priority, becauseweighting coefficient W1 is calculated for Class 1 which is guaranteedthe minimum rate in consideration of the transmission rate of Class 0which is the preferential class.

[0112] In the second embodiment, transmission rate r for preferentialClass 0 may be set at a constant value or may be updated at regular timeintervals. When transmission rate r for Class 0 is updated at regulartime intervals, weighting coefficient calculation unit 35 calculatesweighting coefficients W1, W2 using updated transmission rate r, as amatter of course.

[0113] Also, while the foregoing embodiment has been described inconnection with the network connection system which comprises ratemeasuring unit 36 for measuring transmission rate r for Class 0,information fed back from user terminal 5 may be used to settransmission rate r for Class 0 in weighting coefficient calculationunit 35.

[0114] Third Embodiment:

[0115] Next, description will be made on a network connection systemaccording to a third embodiment of the present invention with referenceto FIG. 7.

[0116] The network connection system according to the third embodimenthas packet scheduling apparatus 44 illustrated in FIG. 7 which issubstituted for packet scheduling apparatus 4 in the network connectionsystem of the first embodiment illustrated in FIG. 4.

[0117] The configuration of packet scheduling apparatus 44 in thenetwork connection system according to the third embodiment of thepresent invention will be described with reference to a block diagram ofFIG. 7. In FIG. 7, components identical to those in FIG. 6 aredesignated the same reference numerals, and repeated description isomitted.

[0118] In the second embodiment described above, IP packets ofpreferential Class 0 are given the highest priority in processingwithout imposing an upper limit thereto. With this strategy, whentransmission rate r for IP packets of Class 0 increases so that thedifference between transmission rate r and packet rate C calculated byoverhead amount correction unit 11 is smaller than minimally guaranteedrate V for Class 1, this minimally guaranteed rate V cannot be assuredfor Class 1. The network connection system of the third embodiment isintended to assure the minimum rate for Class 1 by setting an upperlimit for the preferential class.

[0119] Packet scheduling apparatus 34 in the third embodimentadditionally comprises preferential class upper limit setting unit 46,and weighting coefficient calculation unit 45 which is substituted forweighting coefficient calculation unit 35 of packet scheduling apparatus4 illustrated in FIG. 5.

[0120] Preferential class upper limit setting unit 46 shapes thetransmission rate for preferential Class 0 by imposing upper limit ratep (bps) calculated by the following equation, when transmission rate rfor IP packets of Class 0 increases so that the difference betweentransmission rate r and packet rate C calculated by overhead amountcorrection unit 11 is smaller than minimally guaranteed rate V for Class1, i.e., when C−r<V:

p=C−V

[0121] Preferential class upper limit setting unit 46 additionallynotifies weighting coefficient calculation unit 45 of the value of upperlimit rate p when it is set for Class 0.

[0122] Then, upon receipt of a notice from preferential class upperlimit setting unit 46 indicating that upper limit rate p has been setfor preferential Class 0, weighting coefficient calculation unit 45 inthe third embodiment calculates weighting coefficient W1 for Class 1,which is guaranteed the minimum rate, in accordance with the followingequation:

W 1=V/(C−p)

[0123] Then, weighting coefficient calculation unit 45 calculatesweighting coefficient W2 for Class 2, which is not guaranteed theminimum rate, in accordance with the following equation, as is the casewith the aforementioned first and second embodiments:

W 2=1−W 1

[0124] Also, for guaranteeing minimum rates V1, V2 for Class 1 and Class2, respectively, preferential class upper limit setting unit 46 shapesthe transmission rate for preferential Class 0 by imposing upper limitrate p (bps) calculated by the following equation, when the differencebetween transmission rate r and packet rate C calculated by overheadamount correction unit 11 is smaller than the sum of the minimum ratesV1, V2 guaranteed for Classes 1, 2 (V1+V2), i.e., when C−r<V1+V2:

p=C−(V 1+V 2)

[0125] In this event, weighting coefficient calculation unit 45 appliesweighting coefficients W1, W2 to Classes 1, 2 in proportion to minimallyguaranteed rates V1, V2, as expressed by the following equations:

W 1=V 1/(V 1+V 2),

W 2=V 2/(V 1+V 2)

[0126] Weighting coefficient calculation unit 45 in the third embodimentperforms similar operations to those of weighting coefficientcalculation unit 35 in the second embodiment except when it receives anotice from preferential class upper limit setting unit 46 indicatingthat upper limit rate p has been set for Class 0.

[0127] According to the third embodiment, while an upper limit isimposed to preferential Class 0, the minimum rate can be assured forClass 1 without fail even when the preferential class is introduced.

[0128] While the network connection system of the third embodiment hasbeen described in connection with preferential class upper limit settingunit 46 which shapes the transmission rate for preferential Class 0 withupper limit rate p calculated by p=C−V, the present invention is notlimited to such a shaping scheme. Preferential class upper limit settingunit 46 may shape the transmission rate for a preferential class withwhatever upper limit rate p, as long as the upper limit is set to thetransmission rate for preferential Class 0 such that minimum rate V canbe guaranteed for Class 1.

[0129] For example, when C−r<V, preferential class upper limit settingunit 46 may determine upper limit rate p by decreasing p step by step tosatisfy C−p>V. Conversely, when packet rate C calculated by overheadamount correction unit 11 increases to satisfy 2V<C−p, preferentialclass upper limit setting unit 46 may double the value of p afterconfirming that the doubling of p results in V<C−2p.

[0130] The foregoing first to third embodiments have been described in ascenario in which there are one each of preferential class andbest-effort class, and two quality guaranteed classes which areweighted. The present invention, however, is not limited to thisparticular scheme, but can be applied as well when any number of qualityguaranteed classes, which are weighted, any number of preferentialclasses, and any number of best-effort classes are combined in variousmanners.

[0131] Also, though not shown, packet scheduling apparatuses 4, 34, 44in the first to third embodiments each comprise a recording medium whichhas recorded thereon a program for executing the packet schedulingmethod described above. This recording medium may be a magnetic disk, asemiconductor memory, or any other recording medium. The program is readinto packet scheduling apparatus 4, 34 or 44 from the recording mediumto control the operation of packet scheduling apparatus 4, 34 or 44.Specifically, a CPU within packet scheduling apparatus 4, 34 or 44instructs hardware resources provided therein to perform particularprocessing under the control of the program, thereby implementing theforegoing processing.

[0132] Also, in the first to third embodiments, the present inventionhas been described in connection with the network connection system forconnecting Internet 7 and a plurality of user terminals 5 when ATMnetwork 2, which employs a protocol different from that employed inInternet 7, is interposed between Internet 7 and a plurality of userterminals 5. The present invention, however, is not limited to such aparticular configuration, but can be applied as well to a networkconnection system for connecting a first communication network and aplurality of user terminals when a second communication network, whichemploys a second protocol different from a first protocol employed inthe first communication network, is interposed between the firstcommunication network and the plurality of user terminals.

[0133] Further, while the first to third embodiments have been describedin a situation in which a cell-based DSL is mixed with a packet-basedDSL within telephone central office 6, the present invention can beapplied as well when the cell-based DSL alone or packet-based DSL aloneis installed within telephone central office 6. In the latter case, evenwhen the number of user terminals 5 increases so that a plurality of DSLmultiplexers 1 are connected to ATM network 2, packet schedulingapparatus 4 can be installed for shaping immediately after the entryfrom Internet 7 into telephone central office 6 to save management costand development cost, thereby leading to a reduction in overall cost.

[0134] In the first to third embodiments, overhead amount correctionunit 11 converts DSL rate information 10 from DSL current rate detector20 to packet rate C. When there is only a packet-based DSL, overheadamount correction unit 11 is not needed, as a matter of fact.

[0135] Further, in the first to third embodiments, quality guaranteedclasses have been described with reference to the best-effort class, butthe present invention can be applied as well to a system which does notemploy the best-effort class.

[0136] While preferred embodiments of the present invention have beendescribed using specific terms, such description is for illustrativepurposes only, and it is to be understood that changes and variationsmay be made without departing from the spirit or scope of the followingclaims.

What is claimed is:
 1. A network connection system for connecting afirst communication network and a plurality of user terminals when asecond communication network is interposed between said firstcommunication network and said plurality of user terminals, said secondcommunication network employing a second protocol different from a firstprotocol employed in said first communication network, said systemcomprising: a scheduling apparatus including: an overhead amountcorrection unit for correcting an overhead amount between dataconforming to said second protocol and data conforming to said firstprotocol to convert received information on a rate based on said secondprotocol to a rate based on said first protocol; and a scheduler forshaping a transmission rate for the data conforming to said firstprotocol from said first communication network such that the dataconforming to said first protocol is delivered at a transmission rateequal to or lower than said rate calculated by said overhead amountcorrection unit; a protocol converter for converting data conforming tosaid first protocol after said scheduling apparatus has shaped thetransmission rate therefor to data conforming to said second protocolfor use in said second network; and a multiplexer including a currentdata detector for supplying said scheduling apparatus with said rateinformation as indicative of a currently set reception rate for saiduser terminals, said multiplexer being configured to transmit to each ofsaid user terminals the data conforming to said second protocol fromsaid protocol converter or the data conforming to said first protocolafter said scheduling apparatus has shaped the transmission ratetherefor.
 2. A network connection system for connecting a firstcommunication network and a plurality of user terminals when a secondcommunication network is interposed between said first communicationnetwork and said plurality of user terminals, said second communicationnetwork employing a second protocol different from a first protocolemployed in said first communication network, said system comprising: ascheduling apparatus including: a classification processing unit forclassifying data conforming to said first protocol received from saidcommunication network based on quality guaranteed classes set thereto;an overhead amount correction unit for correcting an overhead amountbetween a data rate associated with said first protocol and a data rateassociated with said second protocol to convert received rateinformation on said second protocol to the rate based on said firstprotocol; a weighting coefficient calculation unit for calculating aweighting coefficient based on said rate calculated by said overheadamount correction unit such that a minimally guaranteed rate is assuredfor a minimum rate guaranteed class among classes classified by saidclassification processing unit; a weighting scheduler for schedulingdata conforming to said first protocol of said minimum rate guaranteedclass and of a weighting applied class among said classified classesbased on the weighting coefficient calculated by said weightingcoefficient calculation unit to deliver the data in accordance with thescheduling; and a scheduler for scheduling the data conforming to saidfirst protocol from said weighting scheduler such that the dataconforming to said first protocol is delivered at a transmission rateequal to or lower than said rate calculated by said overhead amountcorrection unit to deliver the data in accordance with the scheduling; aprotocol converter for converting the data conforming to said firstprotocol after said scheduling apparatus has shaped the transmissionrate therefor to data conforming to said second protocol; and amultiplexer including a current data detector for supplying saidscheduling apparatus with said rate information as indicative of acurrently set reception rate for said user terminals, said multiplexerbeing configured to transmit to each of said user terminals the dataconforming to said second protocol from said protocol converter or thedata conforming to said first protocol after said scheduling apparatushas shaped the transmission rate therefor.
 3. A network connectionsystem for connecting a first communication network and a plurality ofuser terminals when a second communication network is interposed betweensaid first communication network and said plurality of user terminals,said second communication network employing a second protocol differentfrom a first protocol employed in said first communication network, saidsystem comprising: a scheduling apparatus including: a classificationprocessing unit for classifying data conforming to said first protocolreceived from said communication network based on quality guaranteedclasses set thereto; an overhead amount correction unit for correctingan overhead amount between a data rate associated with said firstprotocol and a data rate associated with said second protocol to convertreceived rate information on said second protocol to the rate based onsaid first protocol; a weighting coefficient calculation unit forcalculating a weighting coefficient based on said rate calculated bysaid overhead amount correction unit such that a minimally guaranteedrate is assured for the minimum rate guaranteed class among classesclassified by said classification processing unit; a weighting schedulerfor scheduling data conforming to said first protocol of said minimumrate guaranteed class and of a weighting applied class among saidclassified classes based on the weighting coefficient calculated by saidweighting coefficient calculation unit to deliver the data in accordancewith the scheduling; and a preferential control scheduler for schedulingthe data conforming to said first protocol from said weightingscheduler, and data conforming to said first protocol of a best-effortclass among said classified classes such that the data conforming tosaid first protocol is delivered at a transmission rate equal to orlower than said rate calculated by said overhead amount correction unit,and for preferentially scheduling the data conforming to said firstprotocol from said weighting scheduler, and delivering the dataconforming to said first protocol of the best-effort class at a timingat which there is no data conforming to said first protocol from saidweighting scheduler; a protocol converter for converting the dataconforming to said first protocol after said scheduling apparatus hasshaped the transmission rate therefor to data conforming to said secondprotocol; and a multiplexer including a current data detector forsupplying said scheduling apparatus with said rate information asindicative of a currently set reception rate for said user terminals,said multiplexer being configured to transmit to each of said userterminals the data conforming to said second protocol from said protocolconverter or the data conforming to said first protocol after saidscheduling apparatus has shaped the transmission rate therefor.
 4. Anetwork connection system for connecting a first communication networkand a plurality of user terminals when a second communication network isinterposed between said first communication network and said pluralityof user terminals, said second communication network employing a secondprotocol different from a first protocol employed in said firstcommunication network, said system comprising: a scheduling apparatusincluding: a classification processing unit for classifying dataconforming to said first protocol received from said communicationnetwork based on quality guaranteed classes set thereto; a ratemeasuring unit for measuring a transmission rate for a preferentialclass among said classified classes; an overhead amount correction unitfor correcting an overhead amount between a rate based on said secondprotocol and a rate based on said first protocol to convert receivedrate information on said second protocol to the rate based on said firstprotocol; a weighting coefficient calculation unit for calculating aweighting coefficient based on said rate calculated by said overheadamount correction unit and the transmission rate for the preferentialclass measured by said rate measuring unit such that a minimallyguaranteed rate is assured for the minimum rate guaranteed class amongthe classes classified by said classification processing unit; aweighting scheduler for scheduling data conforming to said firstprotocol of said minimum rate guaranteed class and of a weightingapplied class among said classified classes based on the weightingcoefficient calculated by said weighting coefficient calculation unit todeliver the data in accordance with the scheduling; and a preferentialcontrol scheduler for scheduling the data conforming to said firstprotocol of said preferential class, the data conforming to said firstprotocol from said weighting scheduler, and data conforming to saidfirst protocol of a best-effort class among said classified classes suchthat the data conforming to said first protocol is delivered at atransmission rate equal to or lower than said rate calculated by saidoverhead amount correction unit, and for preferentially scheduling thedata conforming to said first protocol of said preferential class,preferentially scheduling the data conforming to said first protocolfrom said weighting scheduler at a timing at which there is no dataconforming to said first protocol of said preferential class, anddelivering the data conforming to said first protocol of the best-effortclass at a timing at which there is no data conforming to said firstprotocol from said weighting scheduler; a protocol converter forconverting the data conforming to said first protocol after saidscheduling apparatus has shaped the transmission rate therefor to dataconforming to said second protocol; and a multiplexer including acurrent data detector for supplying said scheduling apparatus with saidrate information as indicative of a currently set reception rate forsaid user terminals, said multiplexer being configured to transmit toeach of said user terminals the data conforming to said second protocolfrom said protocol converter or the data conforming to said firstprotocol after said scheduling apparatus has shaped the transmissionrate therefor.
 5. A network connection system for connecting a firstcommunication network and a plurality of user terminals when a secondcommunication network is interposed between said first communicationnetwork and said plurality of user terminals said second communicationnetwork employing a second protocol different from a first protocolemployed in said first communication network, said system comprising: ascheduling apparatus including: a classification processing unit forclassifying data conforming to said first protocol received from saidcommunication network based on quality guaranteed classes set thereto; arate measuring unit for measuring a transmission rate for a preferentialclass among said classified classes; an overhead amount correction unitfor correcting an overhead amount between a rate based on said secondprotocol and a rate based on said first protocol to convert receivedrate information on said second protocol to the rate based on said firstprotocol; a preferential class upper limit setting unit, operative whenthe difference between the transmission rate of the data conforming tosaid first protocol of the preferential class as measured by said ratemeasuring unit and said rate calculated by said overhead amountcorrection unit is lower than a minimally guaranteed rate for a minimumrate guaranteed class among the classes classified by saidclassification processing unit, for setting an upper limit to thetransmission rate for said preferential class for shaping, such that theminimally guaranteed rate can be assured for said minimum rateguaranteed class; a weighting coefficient calculation unit, operativewhen said preferential class upper limit setting unit does not set theupper limit, for calculating a weighting coefficient based on said ratecalculated by said overhead amount correction unit and the transmissionrate for the preferential class measured by said rate measuring unitsuch that the minimally guaranteed rate is assured for the minimum rateguaranteed class among the classes classified by said classificationprocessing unit, said weighting coefficient calculation unit beingfurther operative when said preferential class upper limit setting unitsets the upper limit, for calculating a weighting coefficient based onsaid rate calculated by said overhead amount correction unit and theupper limit rate set by said preferential class upper limit setting unitsuch that the minimally guaranteed rate is assured for said minimum rateguaranteed class; a weighting scheduler for scheduling data conformingto said first protocol of said minimum rate guaranteed class and of aweighting applied class among said classified classes based on theweighting coefficient calculated by said weighting coefficientcalculation unit to deliver the data in accordance with the scheduling;and a preferential control scheduler for scheduling the data conformingto said first protocol of said preferential class, the data conformingto said first protocol from said weighting scheduler, and dataconforming to said first protocol of a best-effort class among saidclassified classes, such that the data conforming to said first protocolis delivered at a transmission rate equal to or lower than said ratecalculated by said overhead amount correction unit, and forpreferentially scheduling the data conforming to said first protocol ofsaid preferential class, preferentially scheduling the data conformingto said first protocol from said weighting scheduler at a timing atwhich there is no data conforming to said first protocol of saidpreferential class, and delivering the data conforming to said firstprotocol of the best-effort class at a timing at which there is no dataconforming to said first protocol from said weighting scheduler; aprotocol converter for converting the data conforming to said firstprotocol after said scheduling apparatus has shaped the transmissionrate therefor to data conforming to said second protocol; and amultiplexer including a current data detector for supplying saidscheduling apparatus with said rate information as indicative of acurrently set reception rate for said user terminals, said multiplexerbeing configured to perform DSL processing using telephone lines totransmit to each of said user terminals the data conforming to saidsecond protocol from said protocol converter or the data conforming tosaid first protocol after said scheduling apparatus has shaped thetransmission rate therefor.
 6. A network connection system forconnecting a first communication network and a plurality of userterminals when a second communication network is interposed between saidfirst communication network and said plurality of user terminals, saidsecond communication network employing a second protocol different froma first protocol employed in said first communication network, saidsystem comprising: a scheduling apparatus including: a classificationprocessing unit for classifying data conforming to said first protocolreceived from said communication network based on quality guaranteedclasses set thereto; an overhead amount correction unit for correctingan overhead amount between a rate based on said second protocol and arate based on said first protocol to convert received rate informationon said second protocol to the rate based on said first protocol; aweighting coefficient calculation unit for calculating a weightingcoefficient based on said rate calculated by said overhead amountcorrection unit and the transmission rate for a preferential class amongsaid classified classes using information fed back from said userterminals such that a minimally guaranteed rate is assured for theminimum rate guaranteed class among the classes classified by saidclassification processing unit; a weighting scheduler for schedulingdata conforming to said first protocol of said minimum rate guaranteedclass and of a weighting applied class among said classified classesbased on the weighting coefficient calculated by said weightingcoefficient calculation unit to deliver the data in accordance with thescheduling; and a preferential control scheduler for scheduling the dataconforming to said first protocol of said preferential class, the dataconforming to said first protocol from said weighting scheduler, anddata conforming to said first protocol of a best-effort class among saidclassified classes such that the data conforming to said first protocolis delivered at a transmission rate equal to or lower than said ratecalculated by said overhead amount correction unit, and forpreferentially scheduling the data conforming to said first protocol ofsaid preferential class, preferentially scheduling the data conformingto said first protocol from said weighting scheduler at a timing atwhich there is no data conforming to said first protocol of saidpreferential class, and delivering the data conforming to said firstprotocol of the best-effort class at a timing at which there is no dataconforming to said first protocol from said weighting scheduler; aprotocol converter for converting the data conforming to said firstprotocol after said scheduling apparatus has shaped the transmissionrate therefor to data conforming to said second protocol; and amultiplexer including a current data detector for supplying saidscheduling apparatus with said rate information as indicative of acurrently set reception rate for said user terminals, said multiplexerbeing configured to perform DSL processing using telephone lines totransmit to each of said user terminals the data conforming to saidsecond protocol from said protocol converter or the data conforming tosaid first protocol after said scheduling apparatus has shaped thetransmission rate therefor.
 7. A network connection system forconnecting a first communication network and a plurality of userterminals when a second communication network is interposed between saidfirst communication network and said plurality of user terminals, saidsecond communication network employing a second protocol different froma first protocol employed in said first communication network, saidsystem comprising: a scheduling apparatus including: a classificationprocessing unit for classifying data conforming to said first protocolreceived from said communication network based on quality guaranteedclasses set thereto; an overhead amount correction unit for correctingan overhead amount between a rate based on said second protocol and arate based on said first protocol to convert received rate informationon said second protocol to the rate based on said first protocol; apreferential class upper limit setting unit, operative when thedifference between the transmission rate for a preferential class amongsaid classified classes determined to be using information fed back fromsaid user terminals and said rate calculated by said overhead amountcorrection unit is lower than a minimally guaranteed rate for a minimumrate guaranteed class among the classes classified by saidclassification processing unit, for setting an upper limit to thetransmission rate for said preferential class for shaping such that theminimally guaranteed rate can be assured for said minimum rateguaranteed class; a weighting coefficient calculation unit, operativewhen said preferential class upper limit setting unit does not set theupper limit, for calculating a weighting coefficient based on said ratecalculated by said overhead amount correction unit and the transmissionrate for the preferential class such that the minimally guaranteed rateis assured for said minimum rate guaranteed class, said weightingcoefficient calculation unit being further operative when saidpreferential class upper limit setting unit sets the upper limit, forcalculating a weighting coefficient based on said rate calculated bysaid overhead amount correction unit and the upper limit rate set bysaid preferential class upper limit setting unit such that the minimallyguaranteed rate is assured for said minimum rate guaranteed class; aweighting scheduler for scheduling data conforming to said firstprotocol of said minimum rate guaranteed class and of a weightingapplied class among said classified classes based on the weightingcoefficient calculated by said weighting coefficient calculation unit todeliver the data in accordance with the scheduling; and a preferentialcontrol scheduler for scheduling the data conforming to said firstprotocol of said preferential class, the data conforming to said firstprotocol from said weighting scheduler, and data conforming to saidfirst protocol of a best-effort class among said classified classes suchthat the data conforming to said first protocol is delivered at atransmission rate equal to or lower than said rate calculated by saidoverhead amount correction unit, and for preferentially scheduling thedata conforming to said first protocol of said preferential class,preferentially scheduling the data conforming to said first protocolfrom said weighting scheduler at a timing at which there is no dataconforming to said first protocol of said preferential class, anddelivering the data conforming to said first protocol of the best-effortclass at a timing at which there is no data conforming to said firstprotocol from said weighting scheduler; a protocol converter forconverting the data conforming to said first protocol after saidscheduling apparatus has shaped the transmission rate therefor to dataconforming to said second protocol; and a multiplexer including acurrent data detector for supplying said scheduling apparatus with saidrate information as indicative of a currently set reception rate forsaid user terminals, said multiplexer being configured to perform DSLprocessing using telephone lines to transmit to each of said userterminals the data conforming to said second protocol from said protocolconverter or the data conforming to said first protocol after saidscheduling apparatus has shaped the transmission rate therefor.
 8. Thenetwork connection system according to claim 1, wherein said currentrate detector periodically applies the rate information to saidscheduling apparatus at regular time intervals.
 9. The networkconnection system according to claim 1, wherein said current ratedetector applies the rate information to said scheduling apparatus whenthe set rate based on said second protocol is updated.
 10. The networkconnection system according to claim 1, wherein said current ratedetector supplies said scheduling apparatus with said rate informationas indicative of a transmission rate set between a user terminal andsaid multiplexer in the event of hand-shaking.
 11. The networkconnection system according to claim 1, wherein said first communicationnetwork is an IP network, said data conforming to said first protocol isan IP packet, said second network is an ATM network, and said dataconforming to said second protocol is an ATM cell.
 12. A traffic shapingmethod, in a network connection system for connecting a communicationnetwork and a plurality of user terminals, for shaping a transmissionrate for data conforming to a first protocol from said communicationnetwork, said method comprising the steps of: classifying dataconforming to said first protocol received from said communicationnetwork based on quality guaranteed classes set thereto; correcting anoverhead amount between a rate based on a second protocol and a ratebased on said first protocol to convert received rate information onsaid second protocol to the rate based on said first protocol;calculating a weighting coefficient such that a minimally guaranteedrate is assured for a minimum rate guaranteed class among saidclassified classes based on said calculated rate; scheduling dataconforming to said first protocol of said minimum rate guaranteed classand of a weighting applied class among said classified classes based onthe calculated weighting coefficient to deliver the data in accordancewith the scheduling; and scheduling the data conforming to said firstprotocol after said weighting, and data conforming to said firstprotocol of a best-effort class among said classified classes, such thatthe data conforming to said first protocol is delivered at atransmission rate equal to or lower than said calculated rate, and forpreferentially scheduling the data conforming to said first protocolafter said weighting, so that the data conforming to said first protocolof said best effort class is delivered at a timing at which there is nodata conforming to said first protocol after said weighting.
 13. Atraffic shaping method, in a network connection system for connecting acommunication network and a plurality of user terminals, for shaping atransmission rate for data conforming to a first protocol from saidcommunication network, said method comprising the steps of: classifyingdata conforming to said first protocol received from said communicationnetwork based on quality guaranteed classes set thereto; correcting anoverhead amount between a rate based on a second protocol and a ratebased on said first protocol to convert received rate information onsaid second protocol to the rate based on said first protocol;calculating a weighting coefficient such that a minimally guaranteedrate is assured for a minimum rate guaranteed class among saidclassified classes based on said calculated rate; scheduling dataconforming to said first protocol of said minimum rate guaranteed classand of a weighting applied class among said classified classes based onthe calculated-weighting coefficient to deliver the data in accordancewith the scheduling; and scheduling the data conforming to said firstprotocol after said weighting, such that the data conforming to saidfirst protocol is delivered at a transmission rate equal to or lowerthan said calculated rate, to deliver the data in accordance with thescheduling.
 14. A traffic shaping method, in a network connection systemfor connecting a communication network and a plurality of userterminals, for shaping a transmission rate for data conforming to afirst protocol from said communication network, said method comprisingthe steps of: classifying data conforming to said first protocolreceived from said communication network based on quality guaranteedclasses set thereto; measuring a transmission rate for a preferentialclass among said classified classes; correcting an overhead amountbetween a rate based on a second protocol and a rate based on said firstprotocol to convert received rate information on said second protocol tothe rate based on said first protocol; calculating a weightingcoefficient based on said calculated rate and the transmission ratemeasured for the preferential class such that a minimally guaranteedrate is assured for a minimum rate guaranteed class among the classifiedclasses; scheduling data conforming to said first protocol of saidminimum rate guaranteed class and of a weighting applied class amongsaid classified classes based on the calculated weighting coefficient todeliver the data in accordance with the scheduling; and scheduling thedata conforming to said first protocol of said preferential class, thedata conforming to said first protocol after said weighting, and dataconforming to said first protocol of a best-effort class among saidclassified classes such that the data conforming to said first protocolis delivered at a transmission rate equal to or lower than saidcalculated rate, and for preferentially scheduling the data conformingto said first protocol of said preferential class, preferentiallyscheduling the data conforming to said first protocol after saidweighting at a timing at which there is no data conforming to said firstprotocol of said preferential class, and delivering the data conformingto said first protocol of the best-effort class at a timing at whichthere is no data conforming to said first protocol after said weighting.15. A traffic shaping method, in a network connection system forconnecting a communication network and a plurality of user terminals,for shaping a transmission rate for data conforming to a first protocolfrom said communication network, said method comprising the steps of:classifying data conforming to said first protocol received from saidcommunication network based on quality guaranteed classes set thereto;measuring a transmission rate for a preferential class among saidclassified classes; correcting an overhead amount between a rate basedon said second protocol and a rate based on said first protocol toconvert received rate information on said second protocol to the ratebased on said first protocol; when the difference between said measuredtransmission rate of the data conforming o said first protocol of thepreferential class and said calculated rate is lower than a minimallyguaranteed rate for a minimum rate guaranteed class among saidclassified classes, setting an upper limit to the transmission rate forsaid preferential class for shaping such that the minimally guaranteedrate can be assured for said minimum rate guaranteed class; calculatinga weighting coefficient based on said calculated rate and saidtransmission rate measured for the preferential class such that aminimally guaranteed rate is assured for said minimum rate guaranteedclass, when the upper limit rate is not set for said preferential class,and calculating a weighting coefficient based on said calculated rateand said set upper limit rate such that the minimally guaranteed rate isassured for said minimum rate guaranteed class when the upper limit rateis set for said preferential class; scheduling data conforming to saidfirst protocol of said minimum rate guaranteed class and of a weightingapplied class among said classified classes based on said calculatedweighting coefficient to deliver the data in accordance with thescheduling; and scheduling the data conforming to said first protocol ofsaid preferential class, the data conforming to said first protocolafter said weighting, and data conforming to said first protocol of abest-effort class among said classified classes such that the dataconforming to said first protocol is delivered at a transmission rateequal to or lower than said calculated rate, preferentially schedulingthe data conforming to said first protocol of said preferential class,preferentially scheduling the data conforming to said first protocolafter said weighting at a timing at which there is no data conforming tosaid first protocol of said preferential class, and delivering the dataconforming to said first protocol of the best-effort class at a timingat which there is no data conforming to said first protocol after saidweighting.
 16. A traffic shaping method, in a network connection systemfor connecting a communication network and a plurality of userterminals, for shaping a transmission rate for data conforming to afirst protocol from said communication network, said method comprisingthe steps of: classifying data conforming to said first protocolreceived from said communication network based on quality guaranteedclasses set thereto; correcting an overhead amount between a rate basedon a second protocol and a rate based on said first protocol to convertreceived rate information on said second protocol to the rate based onsaid first protocol; calculating a weighting coefficient based on saidcalculated rate and the transmission rate for a preferential class amongsaid classified classes determined to be using information fed back fromsaid user terminals such that a minimally guaranteed rate is assured fora minimum rate guaranteed class among said classified classes;scheduling data conforming to said first protocol of said minimum rateguaranteed class and of a weighting applied class among said classifiedclasses based on said calculated weighting coefficient; and schedulingthe data conforming to said first protocol of said preferential class,the data conforming to said first protocol after said weighting, anddata conforming to said first protocol of a best-effort class among saidclassified classes such that the data conforming to said first protocolis delivered at a transmission rate equal to or lower than saidcalculated rate, preferentially scheduling the data conforming to saidfirst protocol of said preferential class, preferentially scheduling thedata conforming to said first protocol after said weighting at a timingat which there is no data conforming to said first protocol of saidpreferential class, and delivering the data conforming to said firstprotocol of the best-effort class at a timing at which there is no dataconforming to said first protocol after said weighting.
 17. A trafficshaping method, in a network connection system for connecting acommunication network and a plurality of user terminals, for shaping atransmission rate for data conforming to a first protocol from saidcommunication network, said method comprising the steps of: classifyingdata conforming to said first protocol received from said communicationnetwork based on quality guaranteed classes set thereto; correcting anoverhead amount between a rate based on a second protocol and a ratebased on said first protocol to convert received rate information onsaid second protocol to the rate based on said first protocol; when thedifference between the transmission rate for a preferential class amongsaid classified classes determined using information fed back from saiduser terminals and said calculated rate is lower than a minimallyguaranteed rate for a minimum rate guaranteed class among saidclassified classes, setting an upper limit to the transmission rate forsaid preferential class for shaping such that the minimally guaranteedrate can be assured for said minimum rate guaranteed class; calculatinga weighting coefficient based on said calculated rate and thetransmission rate for the preferential class such that the minimallyguaranteed rate is assured for said minimum rate guaranteed class, whenthe upper limit rate is not set for said preferential class, andcalculating a weighting coefficient based on said calculated rate andsaid upper limit rate set for said preferential class such that theminimally guaranteed rate is assured for said minimum rate guaranteedclass, when the upper limit rate is set for said preferential class;scheduling data conforming to said first protocol of said minimum rateguaranteed class and of a weighting applied class among said classifiedclasses based on said calculated weighting coefficient; and schedulingthe data conforming to said first protocol of said preferential class,the data conforming to said first protocol after said weighting, anddata conforming to said first protocol of a best-effort class among saidclassified classes such that the data conforming to said first protocolis transmitted at a transmission rate equal to or lower than saidcalculated rate, preferentially scheduling the data conforming to saidfirst protocol of said preferential class, preferentially scheduling thedata conforming to said first protocol after said weighting at a timingat which there is no data conforming to said first protocol of saidpreferential class, and delivering the data conforming to said firstprotocol of the best-effort class at a timing at which there is no dataconforming to said first protocol after said weighting.
 18. The trafficshaping method according to claim 12, wherein said first communicationnetwork is an IP network, said data conforming to said first protocol isan IP packet, said second network is an ATM network, and said dataconforming to said second protocol is an ATM cell.